This invention relates to the method and apparatus for cleaning pipe, and more particularly to such a method and apparatus for cleaning the outside of the pipe as the apparatus moves along the pipe.
Heretofore, self propelled apparatus has been provided, such as shown in U.S. Pat. No. 4,603,516 for cleaning the outside of pipe as the apparatus moves along the pipe while supported thereon. Cleaning the outside of pipe removes loose rust, scale and dirt, to prepare the pipe for the subsequent application of a coating material on the outer surface of the pipe to minimize corrosion and prolong the service life of the pipe. In some instances, the pipe may be wrapped with an outer lining material containing an inner coating material for contacting the outer cleaned surface of the pipe. Normally abrasive particles, such as hard shot particles or grit, has been thrown by centrifugal force from an impeller wheel or the like against the outside of the pipe for cleaning the pipe. Particularly where hard shot particles of a uniform size were used previously, a relatively smooth clean outer surface of pipe was provided.
It is desirable to have a roughness on the outer surface of the pipe to provide a strong bond between the pipe and coating. The roughness increases the surface area of the pipe in contact with the coating for "anchoring" the coating on the pipe. Such an increased area bond is particularly needed upon an expansion of the pipe resulting from pressure or temperature increases to maintain the bonding contact between the pipe and coating. The greater the roughness, the stronger the bond between the pipe and coating particularly for shearing stresses.
A blast chamber on a self propelled carriage travelling along the pipe has been utilized previously but such carriages have been relatively complex for carrying blast wheels or impellers and for assembly on and disassembly off the pipe.